Graphic data devices are commonly employed in areas such as facsimile transmission and computer data input. Earlier forms of such devices employed a stylus or cursor in the form of a writing implement or pointer device mechanically coupled to a set of arms for translating the movement thereof into a sequence of usable information signals. Such arrangements proved unsatisfactory in that undesirable frictional and inertial limitations reduced accuracy. One variation of the foregoing arrangement employed a sheet resistance material to provide an X/Y coordinate indication, but such devices often presented resolution and uniformity problems giving rise to erroneous information. Other forms, such as light pens, may provide graphical data. But they require interaction with cathode ray display tubes and thus are limited in usefulness. One attempt made to overcome the difficulties has been the employment of a sonic transducing coordinate digitizer requiring some form of acoustic transmission, either through the atmosphere or through the surface to set a receptor or like devices. The signal source can be a vibrational or sonic wave generation device. The vibrational device operates conventionally by the use of a tuned crystal generator and pick-up devices acoustically coupled to the sub-surface of a two dimensional digitizing area. The accuracy of tuning is important in such devices and requires extensive constructional detail and expensive components.
The sonic wave generation devices rely upon atmospheric transmission of a sound wave generated at the location determined by the sound source with respect to the sound receivers. Use of atmospheric transmission, however, has proven to give rise to inaccuracy, non-uniformity and loss of resolution as a result of variation in effective ambient conditions. The speed of sound will vary considerably over temperature range, and is necessary to provide some means of temperature compensation in order to provide accurate reproducibility of coordinate digitization using an atmospheric transmission system. In addition, the atmospheric transmission system is subject to Doppler effect error and propagation time error due to draft conditions, and to external noise conditions, all resulting in erroneous information. Finally, atmospheric transmission systems require a specific sound source, which often proves objectionable from a noise level viewpoint, as well as in providing certain discomfort and inconvenience, particularly in light of the requirement of an audible sound source to be positioned at the tip of a writing stylus handheld by an operator.
Another alternative has been an array of embedded wires positioned in a data surface or subsurface along X/Y coordinates. In the embedded wire system, the stylus provides some means for generating a magnetic field, which is picked up in the location corresponding to the closest coordinate intersection of the X/Y position in the subsurface. The signal thus transduced into the data surface wire array is picked up by means of a suitable receptor located at the end of the respective wires and the position of the respective wires is thereafter digitized. Conventional means for accomplishing the foregoing have employed digital logic circuitry responsive to the presence of induced pulses along the appropriate X/Y wire lines corresponding to the position of the transduced pulses. Unfortunately, this system is not absolute, but rather digitizes only with respect to an initial position.
An alternative to the foregoing form employs the use of delay lines terminating the X/Y array. The time delay required for the pulse induced in an X/Y wire to traverse the delay line from the termination of the respective X/Y wire to a point where a device senses the pulse on the delay is measured, provides a measure of the coordinate location. In the past such delay lines were often ordinary delay cables such as illustrated in U.S. Pat. No. 3,648,277.
Another attempted solution has been to use magnetostrictive lines. These lines can be used either as a substituted for the delay line terminating the array X/Y wires or as the wires in the X/Y array itself. An example of the latter application is U.S. Pat. No. 3,846,580. Unfortunately, the sensing means required to respond to the vibrational signal on the magnetostrictive line has presented problems. Either the pick up is too sensitive and detects noise or is not sufficiently sensitive to adequately detect the propagating vibrational signal. Another problem is that magnetostrictive tablets require that they be periodically wiped with a permanent magnet to initialize the magnetostrictive wires. This wiping operation also had to be performed when any magnetic material came too near the tablet and created a dead spot.
It is therefore an object of the present invention to provide an improved coordinate data device.
It is another object of this invention to provide a coordinate data device employing pulse generation and pick up on absolute coordinate basis.
It is a further object of the invention to employ prior art magnetostrictive techniques with an improved signal sensing device.
It is another object of this invention to provide such an improved signal sensing device for a coordinate data device having higher accuracy and more reliability than those heretofor available at an economical cost.
The foregoing objects are realized in a position determining device with the provision of array of plurality of transmission data. Transmission media preferably consist of an array of closed loop wire conductors arranged along a horizontal or X axis and a further array of closed looped wire conductors arranged along a vertical or Y axis. A stylus or cursor movable over the surface produces a magnetic flux to couple the stylus to the aforesaid wire conductors. When energized the stylus induces an electrical current in the closest of the conductors. A longitudinal magnetostrictive element with its axis transverse to said conductors has induced therein a longitudinal strain wave by electrical current in the conductor. The strain wave propagates along the axis of the magnetostrictive element. Near the end of the magnetostrictive element is sensing means for generating an arrival signal in response to the strain wave traversing its location. In particular the sensing means includes a lumped inductive-capacitive delay line substantially aligned with the magnetostrictive delay line. The delay in the lumped delay line is adjusted to be equal to the delay of the magnetostrictive line over the distance of magnetostrictive line which is covered by the lumped delay line. The lumped delay line is defined by the formulas ##EQU2## where T.sub.d is the delay time in the lumped delay line, V is the velocity of sound in the magnetostrictive element, W is the length of the lumped delay line, and ##EQU3## where Z is the delay line's terminating impedance, L is the total inductance of the delay line and C is the total capacitance of the delay line.